Process of concentrating aqueous liquids.



E. COLLETL PP JCESS 0F CONCENTRATING AQUEOUSLI QUIDS. APPLICATION FILEDNOV. 25. M3.

Patented. May 30, 1916.

tical manner.

1.: a artr EMIL COLLETT, OF CHRISTIANIA, NORWAY, ASSIGNOR TO NORSKHYD-RO-ELEKTRISK KVAELSTOFAKTIESELSKAB, 0F (3HHISTULNIJ'X, NORWAY.

PROCESS CONCENTRATING AQUEOUS LIQUIDS.

Specification of Letters Patent.

Patented May 30, 11916.

To all whom it may concern Be it known that I, E'MIL (oLLn'rn a subjectof the King of Norway, residing at (hristiania, Norway, have inventedcertain new and useful. Improvements in Processes of ConcentratingAqueous Liquids; and I do hereby declare the following to be a full,clear, and exact description of the invention, such as will enableothers skilled in the artto which it appertains to make and use thesame.

This invention has for its object a process of drying liquids, gases andvapors.

It is known to concentrate aqueous liquids by mixing the same withdrying agents and then expelling the same. from the mixture by treatingthe latter in opposed current with hot gases, steam, etc. The knownprocesses, however, have several drawbacks and imperfections. Thus ifusing hot gases for expelling the liquids to be concentrated.

the vapors obtained will be mixed up and diluted with these gases andthe condensing apparatus will consequently be excessively large; ifsteam be used, the drying agents will thereby be highly diluted so thatin concentrating the same not only the water absorbed from the liquidbut also the ater from the condensed steam will have to be removed. Ithas also been proposed to bring vapors in a different manner, 6. g. inaccordance with common practice in laboratories, into contact withdrying agents for the purpose of obtaining a concentration of thevapors. Various difficulties, however, are thereby encountered, e. g. onaccount of the reaction between the diluted vapors and the drying agentsthe latter will be excessively heated, or if part of the reaction heatbe removed by cooling at all points where the vapors and the dryingagentare in contact with each other, the drying agent will absorb aportion of the vapors whereby losses will arise owing to the fact thatthe drying agent on leaving the drying apparatus will carry with it aportion of the liquids supplied. It is a matter of great importance toavoid such loss in a prac- Also it is of great importance to rationallyutilize the heat set free by the reaction between the evaporated diluteliquid and the drying-agent. The

ways hitherto adopted to utilize said heat have not proved to beadvantageous.

Applicant has now found that for drying aqueous liquids, such as dilutenitric acid, in the most rational manner, the process may be adoptedwhich is hereinafter described: The nitric acid to be concentrated isboiled in a distilling apparatus adapted for indirect heating, e. g. aboiler with external heating. The nitric acid vapors thereby formed areconducted to a drying apparatus in opposed current with a drying agent,such as sulfuric acid, whereby the water of the vapors, if thetemperature in the apparatus is a suitable one, will be taken up in thesulfuric acid so that vapors of pure concentrated nitric acid willescape from the drying apparatus. Said nitric acid is then condensed insuitable apparatus.

In such an apparatus the following process will take place, providingthat it operates as desired, that is, that the nitric acid vapors, thatescape, are practically free from water. In the top part of theapparatus nitric acid vapors mixed with some aqueous vapor willencounter sulfuric acid of high concentration. As the sulfuric acid willabsorb-aqueous vapor, heat will be developed. The lower. the point atwhich this takes place in the apparatus, the greater the development ofheat. Simultaneously with absorbing water, however, the sulfuric acidwill also absorb some nitric acid especially if it is cold. If thistakes place in the top part of the apparatus it will have no essentiallydetrimental eifect on the process, for the matter especially ofimportance in said portion of the apparatus is that the nitric acidvapor may escape practically free from water. It is not prejudicial forthis purpose that the temperature of the sulfuric acid in the topportion of the apparatus differs considerably from the temperature ofthe nitric acid vapors which it encounters, on the contrary, this willincrease the drying effect of the acid. In the bottom portion of theapparatus highly aqueous nitric acid vapors will encounter dilutesulfuric acid, containing considerable quantitles of nitric acid(absorbed in the course of the process)- The sulfuric acid having atthis point but little capacity of absorbing water fromthe nitricacidvapors, the object of this part of thejapparatus is materiallydifferent from that of the top portion of the apparatus. Since thesulfuric acid that leaves the apparatus, must be freed of its content of'Iiitficacidjbefore it is subjected to concentration, innrtler that itmay againbeintroduced in the apparatus at the top of the. sal ne,' it ia matter of importance that its content of nitric ,.ac-idshould be smallas possible. It is therefore the main object of the bottom portion ofthe apparatus to free thesulfuric acid of the nitric acid absorbed inthe course of the process.

This maybe attained by maintaining the temperature in this portion ofthe appa- 'ratus as high as possiblewithout causing a.

dissociation of the nitric acid. At this high temperature most of thenitric acid contained in the sulfuric acid is eXpelled, and

said nitric acid vapors will ascend, together I with those that havebeen introduced in the apparatus, into the central; portion of the It ischiefly in this portion ofapparatus. the apparatus (the central portion)that the drying of the nitric acid vapors takes place.

By the sulfuric acid absorbing water such a considerable amount of heat.is developed that the process, as is well known, cannot be carried outin a rational manner without the use of a rather energetic cooling. Nowin order to enable the cooling of the ap- I 'paratus to be'eifected insuch a way that the above-mentioned useful "working conditlons forthetwo extreme portions may be obtained, the process isfadopted accordingto the invention that, at a suitable point of the apparatus, so much hotliquid is withdrawn' whi'ch is again introduced I in cooled condition ata higher -pointthat .the

amount'of heat removed by the coolingwill' correspond to the heatdeveloped in the drying zone proper. Since there should preferably besulfuric acid (.or .some other drying agent) of the highest possibleconcentration in the very top portion of the apparatus, it I ispreferred to introduce the cooled liquid above referred to (which willgenerally contain a considerable amount of Water) "not at the top of theapparatus, but' at a point lower down, the concentrated s11.-

' furic acid beingintroduced in a cold condition; at the top. If theapparatus is operated in this manner, a zone will consequently beobtained in thesame, in which, besides the liquid passing through theapparatus,-a constant quantity of liquid will" circulate the object ofwhich is a double one: to act as a drying agent together with thecomparatively slight quantity of concentrated drying agent which isconstantly added, at the top, and to maintain the temperature in thisportion of the apparatus so low as to enable the drying agent to .per-

form its work'at its degree of concentration The-system abpye describedis notin itself complete. To make it 'complete*therewill- .have to beconnected with the apparatus 'deof the sulfuric .acid flowing out at thebotapparatus.

'tion of the heat set free in the drying apparatus will be directlyutilized.

conducted through the distilling apparatus together with the vapors fromthe same,'t'o

at that point. Besides'cboling this liquid While ,it is circulating, itspercentum com- I position may also if desired be varied by a suitableprocess (6'.

i g. removing nitric acid by denitration).

ing agent on leaving the drying apparatus nearly free, from nitric acid.Stiii quite small quantities of nitric acid, however, will easily becarried along therewith. Tov recover thesame. a denitration may becarried out in the usual manner directly in 1 connection with the dryingprocess. This may be efiected-by conducting the drying. i I .agentpassing from the drying apparatus,

to a denitrating column in which the denitration takes place in a knownnianner. Since, however, thequantities of nitric acid contained in thedrying agent, are small, and the temperature of the drying agent ishigh, the denitration in this case may be obtained by blowing in smallquantities of cold air. In this way an essential propor- 10c An important po nt of the present process is, moreover, the manner in which thevapors from the dBIIltlfltlIlg apparatus are treated. The same mayeither be conducted directly into,

the drying apparatus'and through the latter in order to be condensedtogether with the bulk of the nitric acid. Or they maybe the dryingapparatus' :Finally the vapors I of denitration may, also be condensedand suppliedtothe drying apparatus at a suitable pointwhereby alsoacooling of the I drying apparatus is attained. By this process allthe-nitric acid supplied to the dis-'' tilling apparatus and eVaporatedin the same, is obtained as concentrated acid. The drying agent passingfrom the dry ing apparatus'may also be treated in a dif-- ferent manner,from the one above described, as it can be caused to flow directly tothe distilling apparatus if desired in mixture with the nitric'acid tobe concentrated. In this case the nitric acid is' distilled fromthemixture, only mixedwith relatively small amountsof aqueous vapor. thebulk of water beingabsorbed by the drying agent in the distillingapparatus. From -the distilling apparatus the drying 1:0

agent then flows-t0 the denitrating apparatus in which the furthertreatment takes place in the manner above referred to. Of course thedistilling apparatus may also be supplied witha drying agent from othersources than the drying apparatus. By proceeding in this manner lessaqueous vapor is produced in the drying apparatus, while at the sametime less supply of heat is required to the distilling apparatus.

It may also in special instances be of great advantage to utilize theheat contained in the drying agent, passing from the drying apparatus ordistilling apparatus, respectively, and to again concentrate said agent.This concentration is effected by conducting the hot drying agent to aconcentrating apparatus of known construction, for instance aconcentrating column, to which it is supplied at the top of theapparatus, the necessary quantity of air or other gases being blown inat the bottom and according to circumstancesin a heated condition. Thevapors issuing from the concentrating apparatus of course in this caseare not conducted into the drying apparatus, but are separatelycondensed, and since they may contain small quantities of nitric acid,the condensate is suitably used for the production of nitric acid, itbeing conducted to those apparatus in which for instance the absorptionof nitrous gases from electric furnaces takes place.

As a drying agent in the processes above described is suitablyemployedsulfuric acid; as a matter of course also other water-binding substancesmay bensed, such as for instance phosphoric acid, arsenic acid,anhyjdrous nitrates, etc.

In the drawing, 1 is a distilling vessel, 2 is the drying apparatus, and3 is a denitration column. The vessel 1 is heated by means of steam orother suitable heating agent supplied to the jacket 4 surrounding thevessel. Dilute nitric acid-is introduced at 5. Nitric acid vapors leavethe vessel through the pipe 6 and are introduced into the drying columnat 7. Concentrated sulfuric acid is introduced into the drying column at8. Concentrated nitric acid vapors leave the column at 9 and pass intothe condenser 10. At a point 11 situated at a distance from the bottomof the column corresponding to about one-third of the length of thecolumn a quantity of drying agent is withdrawn. The liquid is drawnthrough a cooler 12, from which it is "forced by means of a pump 13 intothe column at a point 14 distant from the top of the column aboutone-third of the whole length of the same. Dilute sulfuric acid flowsout from the drying column through the pipe 16 and is-introduccd intothe denitration column either directly, or indirectly by way of pipe 17,the

vessel 1, and pipe 18. Vapors from the de-- nitration column pass eitherdirectly into the condenser 19, or through pipe 20 back -into the dryingcolumn at 7. Hot gases or vapors are introduced into the denitr'ationcolumn at 21.

hen working in the manner above described, not only the advantageshereinbefore referred to are obtained above the known methods, namely,that the ,denitrat ing apparatus may be made very small or be entirelydone away with, that the drying may be efi'ected with a minimum amountof drying agent, and that a quantitative output of the nitric acld isobtained, but also the fact that on account of the rational utilizationof the apparatus the plant may be given the smallest possible dimensionsso that the expense of construction and operation will be considerablyreduced.

I claim 1. The process of concentrating aqueous liquids which consistsin evaporating the liquid by indirect heating, conducting the vapors soobtained to the lower end of a drying apparatus charged with dryingagent and maintaining the middle portion of the said'apparatus at atemperature suitable for the drying process by drawing ofi at a suitablepoint a portion of the liquid flowing down through the apparatus,cooling it and introducing it again at a higher point in the apparatus.

2. The process of concentrating aqueous liquids which consists 1nevaporating the liquid by indirect heating, conducting the ing drawn offfrom the apparatus at such a distance above the lower end of the samethat the temperature below this point becomes sufficiently high toeffect the evaporation .of the Water taken up by the drying agent sothat this latter leaves the apparatus in the purest possible condition.

apparatus, the said portion of the liquid be- 3. The process ofconcentrating aqueous liquids which consists in evaporating the liquidby indirect heating, conducting the vapors so obtained to the lower endof a drying apparatus charged with drying agent and maintaining themiddle portion of the said apparatus at a temperature suitable for thedrying process by drawing off at a suitable point a portion of theliquid flowing down through the apparatus, cooling it and introducing itagain at a higher point in the apparatus, maintainingthe highlyconcentrated drying agent introduced at the top of the apparatus at sucha low temperature,

ram

that thecooling liquid could be introduced only at a certain distancefrom the upperv end whereby the vapors in the upper part of theapparatus (are subjected only to a most energetically acting dryingagent.

4. Thetprocess ofcon'centrating aqueous liquids which consists inevaporating the. liquid by indirect heating, conducting the vapors soobtai'nedto the lower end of a drying apparatus charged with dryingagent, and maintaining the middle portion of said apparatus at atemperature suitable for the drying process by drawing off at a suitablepoint a portion of the liquid flowing down through the apparatus,cooling the Withdrawn liquidand introducing-it again .troducing saiddrying agent into thebody of '25 I sists in conducting the drying agentafter having passed through said'a-pparatus and at a higher point in theapparatus, and inliquid to be evaporated, the vapors of said body ofliquid bemg introduced into the drylng apparatus.

- 5. In the process of'concentrating aqueous liquids by causing vaporsof such liquids to come into contact with a liquid drying agent in adrying apparatus, the step which concontaining vapor other than watervaporinto the body of liquid being vaporized for supplying saidapparatus with'vapors to be dried. v

6. The process of concentrating nitric acid, which comprises distillingWeak acid, conducting the vapor thereof to a drying apparatus chargedwith a liquid drying agent, maintaining the middle portion ofsaidapparatus at a temperature suitable-for .the drying process by drawingoff at a suit- ,In testimony that I claim the foregoing as my invention,I have signed my namein presence of two subscribing witnesses.

EMIL COLLETT.

Witnesses:

' M. E. GUBBoRNsEN,

RUTH .LINDsrrAN,

